1. Field of the Invention
The present invention relates to systems for and methods of joining a plurality of workpieces, and more particularly to an improved resistance spot welding system and method for reducing workpiece deformation.
2. Discussion of Prior Art
Resistance spot welding devices are used in various industrial applications, including automotive vehicle body construction. These systems function to transmit an electric current through a plurality of adjacently secured workpieces, such that the resistance of the workpieces generates sufficient heat energy to produce a spot weld therebetween. The assembly is initially secured by first positioning the workpieces in a desired configuration, and then utilizing fixtures to clamp the workpieces together. A typical fixture consists of various types of tooling elements that accurately locate and orient the workpieces with respect to the tool path and restrains workpiece motion in the presence of welding electrode forces.
In automotive sheet metal assembly, part positioning and clamping are typically facilitated by programmable robots within an assembly cell. While a first set of robots apply clamping elements to the workpieces at predetermined datum locations, a separate set of welding robots apply electric current to the workpieces to produce a plurality of dimension control welds (DCW's). The datum locations are typically verified during the construction and installation of the assembly cell, and the DCW's are typically produced as close to the datum locations as possible to minimize workpiece deformation. Due to equipment size and configuration, however, the electrodes are typically unable to produce these welds adjacent the datum location, and must therefore engage the workpieces at locations spaced a minimum distance from the datum locations. Applying compressive welding forces at these non-datum locations result in workpiece deformation, which reduces vehicle dimensional accuracy.
These multi-apparatus systems also present various manufacturing concerns, including overcrowding of floor and three-dimensional space within the assembly cell, increased tooling costs, and longer cycle time. While the former concern directly impacts convenience and efficiency, the later concerns affect overall costs of production.
Accordingly, there is a need in the art for an improved system and method for spot welding a plurality of workpieces that reduces production costs and workpiece deformation.